This invention relates generally to a cylinder provided with a plate gripping and securing device and, in particular, to a plate cylinder for a rotary printing press that utilizes spaced-apart tines to penetrate a trailing leg of the plate to secure the plate to the outer surface of the cylinder.
Various devices for securing flexible plates to cylinders in rotary printing presses are generally known. Typically, the leading and trailing legs of the printing plate are inserted into a narrow, axially extending slot in the surface of the cylinder. The plate legs are held in place by a clamping device that is situated in the interior of the cylinder. For example, as disclosed in U.S. Pat. No. 5,653,170, the clamping device may comprise a rotatable spindle or shaft with radially outwardly extending, spring-biased pressure elements that force the plate legs against a lateral wall of the slot. The pressure applied by the pressure elements holds the plate in place.
A general limitation of this type of prior art device is that the pressure applied to the plate legs by the pressure elements may be overcome allowing the plate to slip on the cylinder. This limitation is particularly pertinent to flexible plates made of polyester or other plastic material, because these materials are inherently slick and not easily held in place by a clamping or pressure force.
It is therefore the primary object of the present invention to provide an apparatus which positively secures a flexible plate to a cylinder.
Another important object of the present invention is to provide an apparatus capable of positively gripping the legs of a flexible plate of plastic or other slick material to secure the plate to a cylinder.
Still another important object of the present invention is to provide such an apparatus which prevents a flexible plate secured to a cylinder from slipping.
Yet another important object of the present invention is to provide such an apparatus for securing a flexible plate on a cylinder which is simple to operate.
A further important object of the present invention is to provide an apparatus which positively secures a plastic plate on a plate cylinder of a rotary printing press.
These and other objects of the present invention are generally achieved by providing a plate cylinder with a narrow slot for receiving the leading and trailing legs of a printing plate, the slot defining a channel that extends in parallelism with the axis of the cylinder. A bore in the cylinder also extends axially thereof and is tangentially in communication with the channel. An operating shaft that carries spaced-apart, axially aligned, radially-extending gripping tines is positioned in the bore and is rotatable between a plate-securing position and a plate-releasing position. When the legs of a flexible plate have been inserted into the channel, the shaft is rotated to the plate-securing position, where the gripping tines contact the surface of the plate""s trailing leg and then penetrate through the trailing leg as the shaft is completely rotated to the plate-securing position. When the shaft is rotated to the plate-releasing position, the tines push the plate""s trailing leg from the channel to release the plate from the cylinder.